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Discussion: |
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Clinical
conditions related to platelet and neutrophil antigens:
Increased
platelet destruction by immune mechanisms is associated with increased
levels of immunoglobulins (usually IgG) or complement on the platelet
surface. Antigenic determinants associated with immune platelet
destruction include the major histocompatibility complex (HLA), the
ABH(O) blood group system, and platelet specific alloantigens such as P1ª¹.
Immune thrombocytopenias may
be caused by alloantibodies (isoimmune), autoantibodies (autoimmune), or
drugs. Immune thrombocytopenia purpura (ITP)
is grouped with autoimmune disorders, although the etiology of
its platelet-associated immunoglobulin is unknown. POST-TRANSFUSION
(ISSOIMMUNE) PURPURA
Post-transfusion (isoimmune) purpura (PTP) is a rare complication
characterized by sudden, profound, and self -limited thrombocytopenia
(less than 20 X 10 9/ L). Bleeding occurs 2 to 12 days after the
transfusion of products containing platelet antigens with the time of
recovery ranging from 5 to 60 days. Most cases have been reported in the
women who lacked platelet-specific antigen P1ª¹ and who had been
sensitized by pregnancy and transfusions. This antigen is located on
platelet membrane glycoproteins III and is present in 97% of the general
population. The antibody produced shows P1ª¹ specificity and fixes
complement in some cases, although not in others. The mechanism
responsible for the destruction of the patient’s P1ª¹-negative
platelets is unknown. After recovery, transfusion with blood containing
the antigen does not always re-stimulate antibody production or cause
thrombocytopenia but have been reported years after the initial episode.
Plasmapheresis appears to be most effective in resolving bleeding
complications, with an increase in the platelet count within 48 hours. NEONATAL
ISOIMMUNE THROMBOCYTOPENIA
Neonatal isoimmune thrombocytopenia is caused by transplacental
passage of maternal IgG antibodies directed against fetal platelet
antigen inherited from the father and absent on the mother’s
platelets. Sensitization to the platelet antigen by previous pregnancies
or transfusions appears unimportant. The disorder is analogous to Rh
hemolytic disease. The infants, born of hematologically normal women,
may have a severe generalized petechial rash or may appear normal at
birth and develop symptoms of thrombocytopenia within 2 to 3 days.
Usually, all hematologic parameters are normal except the platelet
count, which may be 30 X 10 9/L or less. Because maternal platelet IgG
antibodies can be transferred across the placenta and produce neonatal
thrombocytopenia, it is important to differentiate alloimmune and
autoimmune IgG antibodies to select the proper treatment. Assays for
maternal platelet antigen IgG (PA IgG) and serum platelet-bindable IgG
is useful for this purpose. The treatment of choice is transfusion with
maternal platelets washed with ABO- compatible plasma reduce the
likelihood of further transfer of maternal alloantibody to the infant.
In the maternal platelets, the infant receives platelet that the
nonreactive with the alloantibody, regardless of antigen specificity. NEONATAL
ISOIMMUNE NEUTROPENIA Neonatal
isoimmune neutropenia results from transplacental transfer of maternal
IgG antibodies directed against fetal neutrophils. Acquired autoimmune
netropenia has been described and is analogous to autoimmune hemolytic
anemia or immune thrombocytopenic purpura, but not as common.
Antineutrophil antibodies have also been described in collagen vascular
diseases (lupus erythematosus, Felty’s syndrome) and following
transfusion of blood products. Transient neutropenia during the first
hour of hemodialysis is believed to be due to activation of the
complement system and sequestration of neutrophils in the lungs
(Clinical Hematology Principle, Procedure, Correlation,
Lotspiech-Steininger 1992)
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